In general, image processing is any form of signal processing for which the input is an image, such as a photograph or video frame.
Most image-processing techniques involve treating the image as a two-dimensional signal and applying standard signal-processing techniques to it. The output of image processing may be either an image or, a set of characteristics or parameters related to the image. Image processing usually refers to digital image processing, but optical and analog image processing also are possible.
Source: Wikipedia
